A mobile ad-hoc network (MANET) is a wireless network comprised of two or more mobile routers and/or hosts, also known as nodes. Since the nodes are mobile, the network topology can change quite often. Nonetheless, in an ideal ad-hoc network there is almost always connectivity between any two nodes in the network, that is, there is always a path between any two nodes in the network such that information can be transmitted between the two nodes. A disruption/delay tolerant network (DTN) may include a mobile ad-hoc network in which at a particular point in time a path between two nodes may not exist, making the routing of information through the network quite challenging.
The routing problem in a DTN is challenging in several respects. First, as mentioned above, unlike in MANETs, there may never be a contemporaneous end-to-end path from a source to destination and one has to exploit transient contacts between nodes in the network to deliver a data packet. Conventional MANET routing protocols typically fail to deliver packets in such situations. Second, disconnection is often the norm rather than the exception, and therefore, controlled replication of data packets becomes much more important. Third, managing persistent storage and bandwidth-limited ephemeral contacts between the nodes in the network is an integral part of the routing in DTNs.
Real-life networks are seldom purely MANETs or DTNs. They often exhibit varying levels of stability and disruption, in terms of data packet delivery, over space and time. Thus, it is important for a routing process to adapt to the network topology and characteristics, and provide robust performance in terms of the required reliable delivery of data packets. Although several routing processes for DTNs exist, such as epidemic routing, probabilistic forwarding and purging, and future contact prediction, there is a need for a routing process which is simple, reliable, independent of the contacts between the nodes in the network, and capable of application in both DTNs and MANETs.